1. Field of the Invention
The present invention relates to reducing or eliminating the inflow of air into a surgical field that occurs during the time that a surgical instrument is used to introduce fluid into the surgical field.
2. Discussion of Related Art
Alcon Laboratories commercializes the SERIES 2000® LEGACY® phacoemulsifier, which is advertised on its website at www.alconlabs.com. The phacoemulsifier includes a console for the physician or medical technician to operate that is programmed to control the operation cation surgical handpiece by sending appropriate command signals. The applicant is featured on the website with respect to advice that the applicant provides for use with the phacoemulsification surgical handpieces to physicians who use the phacoemulsifier in their medical practice. With respect to infusion, some of the advice found on the website that the applicant provides for the benefit of physicians includes the following:                Although gravity infusion has historically been the standard method for delivering fluid to the eye during phaco, problems with reliability and efficiency exist. These are:                    1. Variable infusion rate depending upon fluid volume within the infusion bottle, Fluid cannot leave the infusion bottle unless it is replaced by air, and this is more difficult when the bottle is relatively full. This is so because the air must travel upward through the entire fluid space, which offers resistance to this exchange. In summary, fluid flows from the bottle with somewhat greater difficulty at the beginning of a procedure than it does at the end of the procedure.            2. The ease with which air enters the infusion bottle is dependent upon the resistance within the “spike vent”. This vent has an air filter and in most designs a check valve to prevent liquid leakage. Both of these offer variable resistance to air flow which is in turn manifest as a variation in infusion capacity and resulting perioperative Iop.                        Gravity infusion is not the only method by which infusion can be delivered to the eye during phacoemulsification or vitreoretinal procedures. The GFI® system, currently available with the ALCON® ACCURUS® phacoemulsification and/or vitrectomy system, delivers infusion by maintaining pressure within an infusion source that does not require elevation above the patient's eye level. Infusion flow is delivered more precisely and accurately with such a system, and this permits the surgeon to maintain absolute control over chamber depth with the simple press of a button.        Two brief preparatory steps should be made before insertion of a phaco tip of a phaco-emulsification handpiece.        With the test chamber in place on the tip, hold the handpiece vertically with the tip aimed at the ceiling. Depress the footpedal into position 3 for 2 seconds. This will remove air which may have remained in the handpiece during preparation, and eliminate the sudden shower of air bubbles into the anterior chamber at the beginning of the procedure.        Check to be certain that the infusion line is securely inserted into the handpiece. Then remove the teat chamber and depress the footpedal into position 1 to verify that infusion flow is both present and appropriate in degree. The handpiece is now ready for use.        Adequate infusion capacity must be maintained by infusion bottle elevation; a drip chamber level of at least 40 inches (100 cm) above the eye should be present.        After achieving nuclear segmentation (or nucleus flipping for those who prefer this technique), set the flow rate at 40-60 cc/mm and 500 mmHg vacuum with the KELMAN Flared MACKOOL ABS tip.        As always, place a second instrument (spatula or chopper)behind the last nucleus segments to be removed in order to protect the posterior capsule in the event of an infusion misdirection syndrome.        
U.S. Pat. No. 5,213,669 ('669 patent), whose contents are incorporated by reference, recognized the risk of thermal injury to the anterior segment of the eye during the use of phacoemulsification. The '669 patent recognized that the implosion of microbubbles during the process generate massive fluid and shock waves that erode the solid material cataractous nuclei, and can release excess thermal energy into the eye. To prevent heat damage, the '669 patent recommended that a constant flow of balanced salt solution in and out of the anterior segment be provided to transfer heat out of the eye and to remove lens debris (lens milk) so that the surgeon can visualize the area. However, any problem with proper balanced salt solution circulation can quickly result in heat damage to eye tissue. To insure proper circulation, the '669 patent recommended that the surgeon should personally perform, among others, the following two steps:
1. Visually be certain that balanced salt solution is being aspirated from the transparent test chamber into the catchment device, that the test chamber remains filled or only slightly dimpled when the device is in phaco mode and held at eye level, and that balanced salt solution exits from the silicone infusion ports before the device is placed in the anterior chamber;
2. Kink the infusion line while in phaco mode and watch for the test chamber to collapse. Follow this by kinking the aspiration line and listen for the sound of vacuum build up.
The present applicant observes that the introduction of air bubbles into the eye is very common during the ultrasonic procedure known as phacoemulsification, and also during non-ultrasonic removal of lens material by irrigation and aspiration. The applicant has performed tens of thousands of phacoemulsification and irrigation/aspiration procedures, and has been able to identify the source of the problem which is as follows.
After preparation of the handpiece for insertion into the eye, air enters the distal portion of the handpiece from the atmosphere either 1) immediately upon the removal of the “test chamber” (a malleable chamber that surrounds the tip of the handpiece and isolates it from the atmosphere), or 2) as the tip is lowered toward the eye and fluid passively drains from the infusion channels in the distal portion of the handpiece and is replaced by atmospheric air. The air travels to the highest portion of the infusion channel to which it can gain access, and remains there until such time during the surgical procedure when it is carried into the eye by infusion fluid. This may occur early in the procedure, but it can be delayed if relatively low infusion flow does not create enough force on the air bubble to pull it away from its tenuous attraction to the inner wall of the infusion channel. It would be desirable to prevent air from entering into the handpiece in the first place, and thereby eliminate the problem.
Although the problem could be eliminated by the maintenance of constant flow of infusion after preparation of the handpiece and beginning immediately with removal of the above described test chamber, this creates the problem of wide dispersion of fluid onto the surgical field as the handpiece approaches the eye. Such dispersion occurs because the usual pressure head within the infusion system (40-90 mm Hg) drives infusion fluid forcefully from the handpiece. This often causes the surgeon to have poor visibility of the surgical organ, or causes the patient to be startled by the sudden rush of fluid onto the portion of the body to be operated upon. Furthermore, the ultrasonic instrument is prepared with a test chamber in place, and even if infusion is activated prior to removal of the test chamber, there is a sudden escape of the pressurized fluid into the atmosphere when the test chamber is removed, and air is therefore still able to gain access into the distal infusion channel as a replacement to the exit of the pressurized infusion fluid.